1. Field of Invention
The present invention relates to a suction gas distribution device for parallel compressor installations.
At least four constraints must be borne in mind when several refrigeration compressors are operated in parallel:                apportioning the oil levels in each compressor;        reducing pressure losses at the suction end in order to maximize the performance factor;        maintaining a minimum flowrate in the pipe to create shear forces that push the oil covering the walls to the compressors; and        total piping cost.        
2. Description of Related Art
The present state of the art offers several existing solutions.
Compressors are often arranged in parallel in refrigeration applications. Oil apportioning systems in this case are complex and expensive, based on combining common oil collectors, devices for measuring individual levels, and solenoid distribution valves. These systems are prohibitively expensive in air-conditioning applications.
Another, less expensive, method consists of forcing the oil return to a compressor and then creating pressure drops at the inlet of each to the compressor to force a balanced oil distribution. The disadvantage of this system resides in the pressure losses generated, which have a direct impact on the energy performance of the cooling system. Moreover, producing several welds to create local pressure losses impacts cost as well as reliability, as the welds increase the risk of leakage.
The following prior art documents describe several solutions for apportioning the oil based on the suction gas distribution mechanism.
U.S. Pat. No. 3,386,262 describes a Y connector and separate flow restriction in a branch line. U.S. Pat. No. 4,729,228 describes a gas flow separator. These two solutions result in an unequal supply of gas and oil to the compressors, with the desired pressure difference equalizing the oil levels through a simple pipe.
U.S. Pat. No. 4,411,141 also shows an oil separation device inside the suction line, and a nonreturn valve in the oil equalization line.
Two other documents, U.S. Pat. No. 4,741,674 and U.S. Pat. No. 4,750,337 relate to parallel compressor arrangements where the suction pressure in the compressor body is kept equal. To achieve this result, U.S. Pat. No. 4,741,674 describes a separate pressure equalization line, different from the oil level equalization line. Valves responding to pressure drops for each compressor are present in the suction distributor to eliminate suction at the inoperative compressors. U.S. Pat. No. 4,750,337 describes a valve arrangement in the suction distributor that ensures pressure equalization in the compressor body.
U.S. Pat. No. 4,551,989 describes a suction distributor arrangement using a T part with a distribution tube mounted below the suction orifices of the compressor bodies, with branch lines connecting the distribution tube to the compressor body and extending perpendicularly to the distribution tube. The dimensions of the branches are designed to allow a sufficient gas velocity for the oil return to the compressor bodies.